Capacitive dome switch

ABSTRACT

This is directed to a dome switch that includes a capacitive sensor. A dome switch can include a dome operative to deform to provide tactile feedback to a user. To provide an electrical instruction to the device, the region underneath the dome can define a free space separating conductive regions forming a capacitor. For example, a tip of the dome, a button placed between the dome and a circuit board, or a user&#39;s finger can form a first conductor of a capacitor, and a support structure for the dome can include a terminal forming a second conductor completing the capacitor. When the dome deflects, the distance between the conductors can change and provide a measurable capacitance variation, which the device can detect. To protect the dome switch from damage due to contaminants, the terminal can be integrated within a volume of the circuit board such that it is not exposed to the environment of the dome switch. In one implementation, the terminal may not be exposed to air.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of previously filed U.S. ProvisionalApplication No. 61/320,718, filed Apr. 1, 2010, which is incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

Users can provide inputs to electronic devices using many differentapproaches. In particular, an electronic device can include one or moretypes of input interfaces including, for example, a button, switch,slider, touch interface, wheel, or combinations of these. In some cases,an input interface can include one or more dome switches. Using atraditional dome switch, a user can at least partially invert a dome toclose an electrical circuit underneath the dome and provide a detectableinput. The dome switch is typically constructed by placing a conductivedome over a contact pad on a circuit board. When the dome is pressed,the dome can invert such that the inner surface of the dome contacts thecontact pad, and provides a conductive path between the periphery of thedome and the contact pad. The dome inversion can also provide a tactile‘click’ that enhances the user's interaction with the switch. A user canactuate a dome switch using any suitable approach including, forexample, by applying a force directly to the dome, or by pressing acosmetic component having a nub that is aligned with the dome.

A dome switch can include one or more openings for allowing air to bedisplaced from underneath the dome when the dome is depressed (e.g., todecrease the air pressure under the dome and provide a desired tactilefeedback). For example, a dome switch can include one or more openingsin a layer provided over the dome for securing the dome to the circuitboard. The openings in the dome switch, however, can provide a path fordebris, water, or other external particles or contaminants to enter avolume underneath the dome and around the contact pad. If contaminantsinfiltrate the volume, the contaminants can cause corrosion or promotethe formation of substances that prevent the proper operation of theswitch. For example, foreign particles can cause rust, oxidation,dendrite growth, or salt, sugar or chemical deposits. As anotherexample, water can infiltrate the internal volume of the dome switch andshort the switch.

SUMMARY OF THE INVENTION

A dome switch that does not rely on direct electrical contact isprovided. In particular, a dome switch having a capacitive sensor fordetecting when a user's finger actuates the dome can be provided.

A dome switch can be formed from a dome placed over a circuit board. Toprovide a signal to an electronic device, the dome can be pressed andinverted. When the dome is inverted, the distance between a summit or atop of the dome and the circuit board can decrease such that opposingconductors positioned on the dome summit and on the circuit board canapproach each other. Detection circuitry or a controller coupled to thedome switch can measure a change in capacitance between the conductorsdue to the change in distance between the conductors, and can interpretthe change in capacitance as a user press of the dome switch.

In some embodiments, the controller can define several capacitancethresholds representing different button presses. For example, a firstthreshold can represent a user placing a finger on the button, while asecond threshold can represent the user pressing the button anddeflecting the dome. As another example, the amount by which a userdepresses the dome can correspond to different thresholds, which cancorrespond to different inputs. In some embodiments, a dome can beconstructed to have a variable resistance to deformation, such that auser can detect tactily several intermediate deformation amounts as theuser depresses the dome.

By using a capacitive sensor to detect an input provided by a user aspart of a dome switch, the components used to provide and detect aninput can be isolated and protected from damage caused by contaminants.In particular, because the different controllers and conductors may notneed to come into direct contact, there may be no conductive interfacebetween the conductors that can be damaged by contaminants (e.g.,water). In fact, the presence of contaminants underneath a dome (e.g.,between a conductor of the dome and a conductor of the circuit board)can have little or no effect on the capacitance detected by acontroller. This can enhance the reliability of the dome switch.Furthermore, the tactile feedback provided by a dome may be easily tunedwithout affecting the electrical performance of the switch by decouplingthe tactile feedback from the electrical detection of an input.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention, its nature andvarious advantages will be more apparent upon consideration of thefollowing detailed description, taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a cross-sectional view of an illustrative dome switchincluding a capacitive sensing mechanism in accordance with oneembodiment of the invention;

FIG. 2 is a cross-sectional view of the dome switch of FIG. 1 when ithas been depressed in accordance with one embodiment of the invention;

FIG. 3A is a cross-sectional view of illustrative capacitive sensingassembly in accordance with one embodiment of the invention;

FIG. 3B is a cross-sectional view of illustrative capacitive sensingassembly when a button is pressed to deflect a dome in accordance withone embodiment of the invention;

FIGS. 4A and 4B are cross-sectional views of illustrative capacitivecapacitor terminals incorporated in an electronic device component inaccordance with one embodiment of the invention; and

FIG. 5 is a flowchart of an illustrative process for constructing acapacitive dome switch for which a conductor is not exposed inaccordance with one embodiment of the invention.

DETAILED DESCRIPTION

An electronic device can include several input interfaces for detectinginputs provided by a user. In particular, an electronic device caninclude one or more dome switches that the user can actuate. FIG. 1 is across-sectional exploded view of an illustrative dome switch including acapacitive sensing mechanism in accordance with one embodiment of theinvention. Switch 100 can include circuit board 101 over which dome 120is placed. Circuit board 101 can include terminal 102 positioned on orin a region of the circuit board that in within a periphery of dome 120.For example, terminal 102 can be positioned on a surface of circuitboard 101, or within a stack of layers combining to form circuit board101. The terminal can have any position relative to dome 120. Forexample, terminal 102 can be located substantially near a center pointor center of mass of a periphery of the dome. As another example, theterminal can be substantially aligned with an apex of the dome, or witha region of the dome that deforms most easily towards the circuit board.

Terminal 102 can be electrically connected to any suitable electronicdevice component to provide a signal indicating that a user has providedan input to dome switch 100 (e.g., that the user has caused dome 120 todeflect). In some embodiments, terminal 102 can be electricallyconnected to a controller operative to detect a change in electricalattributes associated with terminal 102 when dome 120 is depressed. Thecontroller can detect any suitable electrical attribute of the terminalincluding, for example, changes in value or measured values of voltage,current, resistance, power, capacitance, impedance, or combinations ofthese. The particular electrical attribute detected can include directcontact of components with terminal 102 (e.g., direct contact to changeresistance), or indirect interactions with the terminal (e.g., changingthe distance between conductors to change capacitance).

In some embodiments, button 130 can be placed over dome 120, such thatthe dome can be depressed and at least partially inverted by pressingthe button using finger 140. Button 130 can be constructed from anysuitable material including, for example, a metal (e.g., aluminum orstainless steel), plastic, composite material, or combination of these.In some embodiments, button 130 can include one or more particularfinishes corresponding to industrial design requirements or desires forthe electronic device. Button 130 can include any suitable feature forinterfacing with dome 120. In some embodiments, button 130 can include anub, recess, or other feature to control the interface between thebutton and the dome. In particular, one or both of button 130 and dome120 can include corresponding features to ensure the alignment andengagement of the button and dome. The button can be maintained at anysuitable distance 122 from terminal 102 when no force is applied todeflect dome 120. In some embodiments, the particular distance can becontrolled from the one or more features used at the interface betweendome 120 and button 130.

When a user applies a force to the dome, for example via the button, thedome can provide a tactile resistance that the user must overcome to atleast partially invert the dome. The dome shape, size, thickness, andposition can be tailored or tuned to adjust the amount or intensity offeedback provided. For example, a dome can be constructed from a lesselastic material to increase the required force, or the dome diametercan decrease to increase the required force. To ensure that a user'sexperience interacting with the dome switch is satisfactory, it may beimportant to correlate the deflection of the dome switch with anelectronic device operation. In particular, the electronic device shoulddetect an input and perform a corresponding operation when the domedeflection is felt by the user.

In some embodiments, providing a dome switch that operates withoutrequiring an electrical contact between the dome and a circuit board canprovide advantages in tuning the switch to perfect a user's experience.For example, the size, travel, and material used for a dome can bechanged or modified to tune the tactile feel of actuating the domeswitch without modifying or affecting the ability of a controller todetect that the switch was actuated. In particular, if a capacitor isdefined between a terminal in a circuit board and either a button placedover a dome, or a finger placed on a button or dome, the size or travelof the dome, or the dome material may not be relevant to detectingswitch actuation. This approach can therefore facilitate productdevelopment and industrial design, as the electrical functionality ofthe dome switch can be separated from its appearance and tactile feel.

FIG. 2 is a cross-sectional view of the dome switch of FIG. 1 when ithas been depressed in accordance with one embodiment of the invention.Dome switch 200 can include some or all of the features of dome switch100 (FIG. 1) including, for example, circuit board 201, terminal 202,dome 220 and button 230 having some or all of the features of thecorresponding components of dome switch 100. When finger 240 pressesbutton 230, the button can travel towards terminal 202 such that theresulting distance between the button and the terminal is distance 222,which can be less than distance 122 (FIG. 1). Finger 240 may be requiredto apply and hold a particular force on button 230 to cause dome 220 toinvert at least partially, as shown in FIG. 2. When inverted, tip 221 ofdome 222 can approach terminal 202, and in some cases even touch thecontact pad (e.g., to provide an electrical path in non-capacitive basedapproaches).

In some embodiments, capacitive sensing circuitry or a controller can becoupled with or incorporated in switch 100 or 200 to detect an inputwhen a user applies a force to the dome. For example, a controller candetect a change in capacitance or inductance measured at terminal 202when a second conductor or terminal approaches terminal 202 as the domeis depressed. The controller can be integrated with or connected to theswitch using any suitable approach. FIG. 3A is a cross-sectional view ofan illustrative capacitive sensing assembly in accordance with oneembodiment of the invention. FIG. 3B is a cross-sectional view of anillustrative capacitive sensing assembly when a button is pressed todeflect a dome in accordance with one embodiment of the invention.Assembly 300 can include housing 311 forming part of an electronicdevice. For example, housing 311 may be part of one or more surfaces ofan electronic device enclosure. In particular, housing 311 can defineone or more internal or external walls of an electronic device. Housing311 can be constructed from any suitable material. In some embodiments,housing 311 can be constructed at least in part using metallic orelectrically conductive materials such as anodized aluminum, steel,titanium or other metals. In some embodiments, housing 311 can insteador in addition be constructed from the combination of metallic andnon-metallic materials (e.g., metal and plastic), or combinations ofdifferent metallic or conductive materials. In some cases, particularelements of housing 311 can include both metallic and non-metalliccomponents. For example, one or more components can include plasticover-molded on metallic components.

In some embodiments, housing 311 can include button 310 operative to bemove within housing 311 in response to the application of a force by auser. For example, housing 311 can include an opening in which a buttonis received, where the housing includes features (e.g., the shape of theopening) that control the displacement of the button within the housing.In some embodiments, button 310 can be constructed from a conductivematerial, or include a conductive element, while housing 311 can beconstructed from a dielectric or electrically insulating material.

Assembly 300 can include dome 320 positioned between button 310 and asupport structure (e.g., circuit board 315), such that the dome canmaintain the button away from the support structure by a predetermineddistance. The distance can be selected such that the output of acontroller or sensing mechanism corresponds to an output indicating thatno input is provided by a user using the assembly. Dome 320 can bedisposed between button 310 and circuit board 315 using any suitableapproach. In some embodiments, dome 320 can be disposed such that aperiphery of the dome is in contact with a surface of circuit board 315,and a tip of the dome is in contact with a surface of button 310.Alternatively, dome 320 can be reversed, such that the periphery of thedome is in contact with a surface of button 310, and a tip of the domeis in contact with circuit board 315 (e.g., inverted dome 321). Theparticular disposition of the dome within assembly 300 may not matterelectrically, as the purpose of the dome may be limited to providingtactile feedback. This is in contrast with traditional dome switches, inwhich the partial inversion of a dome creates an electrical contact thatcan be detected by a circuit.

Because the tactile feedback provided by the dome can be disassociatedfrom an electrical signal detected by the assembly, dome 320 can haveany suitable shape that provides a tactile feedback to a user. Forexample, dome 320 can include several ridges and valleys (e.g.,concentric domes) that can deform in sequence or in parallel. As anotherexample, dome 320 can include a spring operative to deflect when a forceis applied, and return to its initial position when the force isremoved. Such springs can include, for example, a helical spring,cantilever spring, leaf spring, Belleville washer, torsion spring, gasspring, or a combination of these. In some embodiments, the materialsselected for dome 320 or its equivalent can be selected based on desiredtactile feedback properties.

Assembly 300 can use any suitable approach to detect a force applied tobutton 310. In some embodiments, assembly 300 can include controller 330operative to detect an electrical attribute corresponding to assembly300 in response to a user applying a force to button 310. Controller 330can detect any suitable electrical attribute or a change in any suitableelectrical attribute. For the simplicity of the following discussion,however, assembly 300 will be described in the context of detectingchanges in capacitance resulting from the user pressing button 310 (orapplying a force directly to dome 320, if no button is used). Controller330 can be coupled to any suitable sensor or terminal from which achange in capacitance can be detected. In response to detecting asuitable electrical attribute or a change in a suitable electricalattribute, control circuitry of an electronic device that includes thedome switch can direct the electronic device to perform a particularoperation.

In some embodiments, assembly 300 can include terminals 312A and 312Bcoupled to or integrated within circuit 315. In some embodiments,terminals 312A and 312B can be integrated in other components of theelectronic device including, for example, housing elements, structuralcomponents of the device, or other elements of the electronic devicethat are not necessarily part of the dome switch. Assembly 300 caninclude any suitable number of terminals including, for example just oneterminal, or several terminals. The terminals can be placed at anysuitable position or distance relative to button 310 (e.g., distance d1shown in FIG. 3A). In particular, terminals can be positioned such thatthe capacitance corresponding to each terminal relative to the button orrelative to another terminal is known when the button is not depressed.In addition, the terminals can be positioned to detect the particularlocation of a user's finger on button 310 (e.g., whether the user'sfinger is closer to a center or side of the button) based on capacitancevalues detected at different terminals of the assembly. In someembodiments, one or more terminals can be located away from dome 320(e.g., partially or entirely not within an area enclosed by a peripheryof the dome).

Terminals 312A and 312B can be constructed from any suitable material.In some embodiments, one or both of the terminals can be constructedfrom a conductive material operative to store a charge that can bedetected by an appropriate sensor. For example, the terminals can beconstructed from a metal to constitute a conductor of a capacitor. Inone implementation, each of terminals 312A and 312B can serve asopposing conductors of a capacitor, where portions of circuit 315 canserve as a dielectric between the conductors of the capacitor. Inanother implementation, button 310 or housing 311 (or portions of thebutton or housing that include a conductive component), or a user'sfinger placed over the button or housing can serve as one conductor of acapacitor, and each of terminals 312A and 312B can serve as a secondconductor of different capacitors, where the space or gap between thehousing and the terminals can form the dielectric separating theconductors of the capacitor. In some embodiments, a portion of dome 320(e.g., a tip of the dome) can be used instead of or in addition tobutton 310 as a conductor for a capacitor. In some embodiments, one ormore of housing 311 and terminals 312A and 312B can be electricallygrounded.

To detect changes in capacitance, terminals 312A and 312B can be coupledto controller 315. When button 310 is depressed, dome 320 can deflectsuch that the distance between button 310 and terminals 312A and 312Bcan decrease. The controller can then measure a change in capacitancewithin a capacitor formed from terminals 312A and 312B as conductors.Alternatively, the electronic device can measure a change in capacitancein each of a first capacitor formed from button 310 (or a user's finger)and terminal 312A, and a second capacitor formed from button 310 (or auser's finger) and terminal 312B. The controller can then use the changein capacitance in one or both of the capacitors to detect a particularinput provided using button 310.

A user can apply a force F on button 310 to actuate the switch. The usercan apply force F using any suitable action including, for example, bypressing, tapping, holding, touching, or squeezing button 310 or housing311. Controller 315 can detect force F by measuring a change incapacitance corresponding to a change in spacing between the housing 311and terminals 312A and 312B. In particular, as housing 311 is displaced,the initial distance d1 between each of the terminals 312A and 312B maydecrease to d2A and d2B, respectively. The reduced distance, in somecases combined with a capacitance inherent to a user's finger, canchange the amount of capacitance detected in each capacitor of assembly300. In some embodiments, controller 315 can determine the location atwhich the user is applying force F by determining which of the terminals312A and 312B experience the largest change in capacitance(corresponding to the largest movement in the housing 311 and deflectionin dome 320, or corresponding to the closest proximity of the user'sfinger to the terminals).

Controller 315 can be operative to detect any suitable difference incapacitance or capacitance value between different conductors. Inparticular, the electronic device can define one or more thresholdscorresponding to detected changes in capacitance or capacitance values.For example, the controller can define a first threshold correspondingto a first change in capacitance when a user's finger is placed over adome (e.g., in contact with a button), and a second thresholdcorresponding to a second change in capacitance when the user's fingercauses the dome to deflect (e.g., the user's finger comes closer to thecircuit board). The electronic device can perform different operationswhen a detected capacitance value or a detected change in capacitancevalue reaches each of the capacitance thresholds.

Because the terminals forming conductors of a capacitor do not need tocome into direct electrical contact with the dome, the terminals can beprotected from debris or other contaminants originating from outside ofthe device without affecting the functionality of the dome switch. FIGS.4A and 4B are cross-sectional views of illustrative terminalsincorporated in an electronic device component in accordance with oneembodiment of the invention. Element 400, shown in FIG. 4A, can includecircuit board 401 for supporting one or more electronic devicecomponents and dome 420 placed over the circuit board. For example, oneor more components can be coupled to circuit board 401 using a solderingor SMT process. To form a conductor of a capacitor, circuit board 401can include conductive terminal 402 placed on a surface of the circuitboard. For example, a conductive trace (e.g., copper) can be depositedon circuit board 401. As another example, a conductive coating can beapplied to a region of circuit board 401 corresponding to terminal 402.As still another example, a conductive component can be connected tocircuit board 401 to form terminal 402 (e.g., using soldering or SMT).Terminal 402 can be electrically connected to one or more components ofthe electronic device including, for example, a controller or othercircuitry for detecting capacitance values or changes in capacitancebetween two conductors.

To protect terminal 402 from debris, protective layer 410 can be placedover terminal 402. In some embodiments, protective layer 410 can inaddition be placed over some or all of a top surface of circuit board401, for example to ensure that side walls of terminal 402 are coveredand protected. Protective layer 410 can be constructed from any suitablematerial. In some embodiments, the protective layer can be constructedfrom a plastic (e.g., paralyne), polymer, composite material orcombinations of these. In some cases, it may be desirable for protectivelayer 410 to be constructed from a dielectric material so thatprotective layer 410 does not interfere with the detection ofcapacitance levels corresponding to terminal 402.

In some embodiments, the material used for protective layer 410 can beselected based on mechanical properties of the material to ensure thatterminal 402 can be adequately protected from interference or damage dueto foreign contaminants or particles. For example, the material selectedcan have a stiffness, resistance to abrasions, friction coefficient, orother mechanical characteristics suitable to protect terminal 402. Theparticular material properties can be selected to protect terminal 402from any suitable type of contaminants. For example, the material can beselected based on a type of contaminant or properties of contaminantslikely to reach the terminal in light of the position of the dome switchassembly within the electronic device (e.g., select a material toprotect from water or sweat damage when the dome switch is in an area ofthe device that comes into contact with the user's skin).

Protective layer 410 can be applied to terminal 402 using any suitableapproach. For example, one or more of a powder coating process, vapordeposition, thin film deposition, and liquid dipping can be used. Insome embodiments, a material can instead or in addition be coupled tothe circuit board and terminal using a stand-alone adhesive, or anadhesive integrated with a film (e.g., placing a piece of tape or anadhesive and a film over the circuit board and conductor). In someembodiments, protective layer 410 can be applied such that terminal 402is not exposed to the environment of the dome switch, and in particulardoes not come into contact with air flowing from outside of theelectronic device (e.g., air containing contaminants). In particular, nosurface of the terminal may be exposed.

Element 425, shown in FIG. 4B, can include circuit board 430 andterminal 432, and dome 440 placed over the circuit board, which caninclude some or all of the features of the corresponding components ofelement 400 (FIG. 4A). In contrast with element 400, terminal 432 can beconstructed such that it is within the volume enclosed by circuit board420. In one implementation, circuit board 430 can be constructed byoverlaying several layers of material. To construct terminal 432 withinthe circuit board, the material corresponding to terminal 432 can beinserted in one of the several layers as it is created, and subsequentlycovered by an additional layer of the circuit board. Alternatively, apocket can be constructed within the volume of circuit board 430 (e.g.,core out a pocket through a side wall or exterior surface of the circuitboard) into which material used for the terminal can be provided. Forexample, a conductive material can be inserted in a pocket or receptacleformed within the circuit board volume. Once the material forming theterminal is positioned in the pocket, the pocket can be closed, forexample using a material used for the circuit board (e.g., a dielectricmaterial to electrically insulate the terminal). The resulting terminalcan be isolated from the device environment, and in particular isolatedfrom air originating from outside of the electronic device (e.g., aircontaining contaminants). In particular, no external surface of theterminal may be exposed.

The terminals used for different switch assemblies described herein canhave any suitable size and shape. In some embodiments, the shapeselected for a particular terminal can be selected based oncharacteristics of a controller used to detect changes in capacitance.The particular size and shape of each terminal in a switch assembly canbe the same or vary.

For example, a terminal that is closer to a button's center can besmaller or larger than a terminal that is farther away. The terminalshapes can include, for example, a triangular, square, rectangular,polygonal, circular, elliptical, curved, or arbitrary shape (e.g., aseries of interlocking fingers, or cross-shaped pattern) when projectedin one or more planes (e.g., in a plane of the circuit board). In someembodiments, the size of a particular terminal can be selected to matchthe size of the dome (e.g., the terminal can include a disc sized tosubstantially correspond to the periphery of the dome).

FIG. 5 is a flowchart of an illustrative process for constructing acapacitive dome switch for which a conductor is not exposed inaccordance with one embodiment of the invention. Process 500 can beginat step 502. At step 504, a terminal that is not exposed to a deviceenvironment can be defined. For example, a terminal can be constructedwithin a volume of an electronic device component. As another example,terminal can be constructed on an exterior surface of a devicecomponent, and can be covered by protective layer. At step 506, a domecan be placed over the defined terminal. For example, a dome providing atactile response when a user actuates a button to provide an input tothe electronic device can be aligned with the defined terminal. In someembodiments, a spring mechanism can be used instead of or in addition tothe dome. At step 508, a controller can be connected to the terminal todetect changes in capacitance. For example, a controller can beconnected to the terminal such that the controller can measurecapacitance values or changes in capacitance of a capacitor for whichthe terminal constitutes a conductor. The second conductor of thecapacitor can include, for example, a button, a user's finger placedover the dome, a second terminal that is not exposed within the device(e.g., a second terminal in a volume of a same circuit board), orcombinations of these. At step 510, the controller can measure a defaultor baseline capacitance value for the terminal when the dome is notdeformed. For example, the controller can measure a default capacitancevalue that corresponds to the absence of a user input. The default valuecan then be compared to other capacitance values detected when a userapplies a force to the dome switch. In some embodiments, step 510 can beskipped, and instead performed during operation of the device (e.g.,repeatedly performed). Process 500 can then end at step 512.

In some embodiments, a different mechanism can be used instead of acapacitance sensor to detect a force applied to a dome switch. Forexample, an ultrasonic detector can be used as a proximity sensor todetect the distance between the button and a circuit board (e.g., byemitting and detecting ultrasounds or other sound waves). As anotherexample, a microphone can be used to detect the sound of the domeinverting. In particular, a controller or processor can be calibrated toidentify a particular audible frequency associated with the inversion ofthe dome. In some embodiments, an optical component can be used todetect a button actuation. For example, an optical component can detecta shadow associated with a dome or button, and monitor for a change inthe shadow. In particular, an optical component can monitor for a changein shadow corresponding to a button press. The optical component can beplaced in any suitable location relative to the dome, including forexample under the dome (e.g., looking up into the dome), or to the sideof the dome. In some embodiments, a pressure pad or pressure componentcan be used to detect inputs. For example, a button can be pressed andprovide a force to a pressure pad placed underneath the button. Thebutton can include an extension providing a contact between the buttonand the pressure pad. In some embodiments, the extension can include aspring operative to deflect and allow the button to travel. The springconstant and the pressure pad can be tuned to define the force anddisplacement required from the button to provide an input to the device.

The above described embodiments of the present invention are presentedfor purposes of illustration and not of limitation, and the presentinvention is limited only by the claims which follow.

1. A dome switch comprising: a circuit comprising a terminal, whereinthe terminal is electrically conductive, and wherein no external surfaceof the terminal is exposed; a dome positioned adjacent to the circuit,wherein a portion of the dome is operative to deflect to decrease adistance between the portion of the dome and the terminal; and acontroller electrically connected to the terminal, wherein thecontroller is operative to measure a change in capacitance of acapacitor for which the terminal serves as a conductor when the portionof the dome deflects.
 2. The dome switch of claim 1, further comprising:a housing placed over the dome, wherein the portion of the dome deflectsin response to a force applied to the housing.
 3. The dome switch ofclaim 2, wherein: the housing comprises a conductive component, whereinthe conductive component of the housing forms another conductor of thecapacitor.
 4. The dome switch of claim 2, further comprising: a buttonintegrated in the housing, wherein the button is operative to moverelative to a portion of the housing to cause the dome to deflect. 5.The dome switch of claim 4, wherein: the button comprises a conductiveportion, wherein the conductive portion of the button forms anotherconductor of the capacitor.
 6. The dome switch of claim 1, wherein: thecircuit comprises another terminal, wherein the other terminal isconductive, and wherein the other terminal is electrically isolated fromthe terminal; and the controller is electrically connected to theterminal and to the other terminal, wherein the controller is operativeto measure a change in capacitance of a capacitor for which the terminaland the other terminal serve as conductors.
 7. The dome switch of claim1, wherein: the terminal is integrated within an internal volume of thecircuit board.
 8. The dome switch of claim 1, wherein: the terminalextends from an external surface of the circuit; and the dome switchfurther comprises a protective layer applied over the terminal such thatno surface of the terminal is exposed.
 9. A method for constructing acapacitive dome switch, comprising: defining a terminal that is notexposed to an environment of the dome switch; placing a dome over theterminal, wherein the dome can deflect to change a distance between atip of the dome and the terminal; and connecting a controller to theterminal, wherein the controller is operative to detect a change incapacitance corresponding to the terminal when the dome deflects. 10.The method of claim 9, further comprising: providing a circuit board;and defining an internal region of the circuit board in which theterminal is located.
 11. The method of claim 10, further comprising:coring an internal volume in the circuit board; inserting a conductivematerial in the internal volume to form the terminal; and closing anopening to the internal volume with a non-conductive material.
 12. Themethod of claim 10, further comprising: overlaying a plurality of layersto form a circuit board, wherein at least one of the layers includes anopening; placing a conductive material in the opening to form theterminal; and overlaying at least one layer over the conductivematerial, wherein the plurality of layers surround all external surfacesof the conductive material.
 13. The method of claim 9, furthercomprising: providing a flex circuit; depositing the terminal on anexternal surface of the flex circuit; and covering the terminal with aprotective layer.
 14. The method of claim 13, further comprising:connecting the protective layer to the terminal and to the externalsurface of the flex circuit using an adhesive.
 15. An electronic device,comprising: a support structure; a conductive terminal, wherein theconductive terminal is coupled to the support structure such that no airexternal to the support structure comes into contact with the conductiveterminal; a controller electrically coupled to the conductive terminal,wherein the controller is operative to detect a capacitance valuecorresponding to the conductive terminal; a dome placed adjacent to thesupport structure, wherein the dome can be at least partially inverted;and a housing enclosing the support structure, the conductive terminal,the controller, and the dome, wherein a tip of the dome is in contactwith the housing such that a force applied to the housing can cause thedome to be at least partially inverted.
 16. The electronic device ofclaim 15, further comprising: a second conductive terminal, wherein thesecond conductive terminal is coupled to a portion of the housing. 17.The electronic device of claim 16, wherein: a distance between theconductive terminal and the second conductive terminal changes when theforce is applied to the housing to cause the dome to be at leastpartially inverted.
 18. The electronic device of claim 17, wherein: thecontroller is operative to detect a change in capacitance valuecorresponding to the conductive terminal when the distance between theconductive terminal and the second conductive terminal changes.
 19. Theelectronic device of claim 17, wherein: the distance between theconductive terminal and the second conductive terminal decreases whenthe force is applied.
 20. The electronic device of claim 15, furthercomprising: control circuitry, wherein the control circuitry isoperative to perform an electronic device operation in response toreceiving an indication from the controller that the capacitance valuecorresponding to the conductive terminal has changed.